Tailoring self-assembled monolayers at the electrochemical interface

The main focus of this review is to illustrate the amenability of self-assembled monolayers (SAMs) for functionalisation with different receptors, catalytic materials, biomolecules, enzymes, antigen- antibody, etc for various applications. The review discusses initially about the preparation and characterization of SAMs and tailoring of SAMs by incorporation of suitable recognition elements. A description of how the molecular recognition is achieved through forces like electrostatic, covalent and host–guest interactions is included in the review

Formation of a nickel hydroxide monolayer on Au through a self-assembled monolayer of 5,5'-dithiobis(2-nitrobenzoic acid): voltammetric, SERS and XPS investigations of the modified electrodes

The formation of self-assembled monolayers (SAM) of 5,5'-dithiobis (2-nitrobenzoic acid), DNBA on gold has enabled further derivatization of the electrode surface with functional moieties anchored to the surface bound molecules. A SAM of DNBA was formed on the Au surface. Nickel ions tethered to the SAM-covered Au surface, were subsequently derivatized electrochemically to yield nickel hydroxide overlayers, thereby showing the possibility of preparing ultra-thin films of metal oxides through solution chemistry. The nickel hydroxide surface coverage obtained on bare and SAM-covered electrodes was estimated from voltammetric peaks and it varied from one monolayer to about 300 monolayers. The formation of a monolayer of nickel hydroxide has been achieved for the first time by electrochemical modification. Further, the modified electrodes were subjected to SERS and XPS studies to understand their surface characteristics. Modified electrodes provide a catalytic pathway involving nickel hydroxide for the electro-oxidation of glucose in alkaline solutions

Chemical Synthesis of PEDOT–Au Nanocomposite

In this work, gold-incorporated polyethylenedioxythiophene nanocomposite material has been synthesized chemically, employing reverse emulsion polymerization method. Infrared and Raman spectroscopic studies revealed that the polymerization of ethylenedioxythiophene leads to the formation of polymer polyethylenedioxythiophene incorporating gold nanoparticles. Scanning electron microscope studies showed the formation of polymer nanorods of 50–100 nm diameter and the X-ray diffraction analysis clearly indicates the presence of gold nanoparticles of 50 nm in size

Enzyme immobilization on ultramicroelectrodes through electropolymerization: Effect of polymeric film thickness on teh amperometric response of the electrode

The rapid growth in the science and technology of the biosensors demands improved methods of enzyme immobilization and miniaturization of sensor devices. The formation, on electrode surfaces, of enzyme-entrapped polymer films through electropolymerization from monomer solutions containing the enzyme offers an elegant and reliable approach for enzyme immobilization, especially on ultramicroelectrodes. Platinum ultramicrodiscelectrodes (UMDE) were fabricated in-house and immobilized with glucose oxidase (GOx) enzyme through electropolymerized films of polypyrrole and poly(I,3-diaminobenzene). The UMDE, modified with GOx-trapped polymer film was tested for its amperometric response to glucose in solution. The polymer film thickness was varied from about 10 to 466 nm by controlling the charge required for the electropolymerization and the influence of the polymer film thickness on the amperometric response to glucose was investigated. Moreover, the effect of oxygenation and de-oxygenation of the test solutions on the amperometric response was also examined. The results of the above studies are presented and discussed in this communication

Investigations on kinetics of electrode processes-studies on exponential transient technique to corrosion kinetics

Research efforts are constantly directed towards development of reliable methods for estimation of corrosion rates (icorr) of metals in solution. The present study is an attempt in this direction. Following a brief presentation of the concepts of electrodics and corrosion kinetics, various electrochemical techniques for estimation of icorr have been critically reviewed. The potentialities of the accelerated Tafel plot (ATP) technique – a transient polarization technique – for application to corrosion kinetics are traced. Subsequently the experimental methodology to analyse then –t transient response through slope and intercept measurements proposed earlier for obtaining the kinetic parameters has been described. The results on icorr data obtained from ATP measurements for the chosen corrosion systems, viz., nickel, iron and steels in acids have been presented and compared with the icorr data collected from steady-state polarization and potential - sweep methods. Simulation studies on a model involving a faradaic reaction and double layer charging have been undertaken to delineate the role of double layer charging and understand the observed variation of icorr at low input time-constants in the ATP method. Based on these studies , two new methods for analyzing ATP data have been evolved, which are free from the drawbacks of the intercept-slope method. The ATP data for the corrosion systems under investigation have been subjected to analysis by the two new methods which yielded satisfactory results. Efforts to assess the ATP method for its suitability to study inhibited corrosion reactions are also presented. The inhibition efficiency data resulting for the corrosion of mild steel in sulphuric acid containing thiosemicarbazide indicated the usefulness of the technique. The efficacy of the two new methods of analysis has also been checked by applying to the redox system viz. ferric-ferrous on nickel. The exchange current data are consistent with expectations. Finally, the related exponential transient technique with linear polarization has been described and taken up for experimental confirmation of its utility using ferric-ferrous on nickel as a model system

Application of ion selective electrodes for corrosion monitoring-I:Corrosion of copper

Ion Selective Electrodes IISE) developed recently have established themselves as powerful analytical probes for estimation of ionic species present in trace and ultra trace levels in solution. The ease of operation coupled with high sensitivity has enabled their successful applications in multifarious fields. Studies on the use of ISE for estimation of metallic corrosion by resorting to solution analysis are scarce. The results of evaluation of corrosion of copper in chloride and acetate media have been described. Use of ISE's for estimation of inhibition efficiency has also been attempted. The results have been compared with data obtained from weight loss and atomic absorption spectroscopy

Electrochemical behaviour of neutral red

The electrochemical studies of the dye molecule, Neutral Red (NR) as!'iurne importance in view of its redox characteristics. The oxidised and reduced forms of NR, depending UpOIl the solution pH, undergo different protonation reactions. The electrochemical behaviour of NR (3-arnino-7-dimethylarnino-2-methyl phenazine) has been studied voltarnrnetrically on a glassy carbon electrode at different pR conditions. The investigations indicate that the electroreduction of NR follows a single stage 2e-transfer. Based on the voltammetric data, the diffusion coefficient of NR and the heterogeneous rate constant for its reduction reaction have heen estimated. The results or the above investigations are presented and discussed in this communication which also includes absorption spectral data or NR in the visible image

Sonoelectrochemistry – an emerging area

Ultrasonic (US) radiation in liquid media is known to produce chemical effects with significant acceleration of reaction rates. Influence on US on electrochemical processes-sonoelectrochemistry-is not totally new. Extensive studies have been reported on the relaxation phenomena and structure of electrolyte solutions, with the help of ultrasounds. However, investigations on the influence of ultrasound on electrode reactions and electrosynthesis are of recent origin. Ultrasonic radiation, known to produce cavitation and microstreaming phenomena in liquid media, has resulted in very high current densities and a modified pattern of product yields during electrochemical reactions. Thus, interfacing ultrasound with electrochemistry appears to hold a lot of potential and the field of sonoelectrochemistry is set to make new strides. Recent investigations in this area carried out in our laboratories and elsewhere are reviewed in this communicatio

Corrosion studies of organicdithiol/monothiol derived self assembled monolayer on copper substrate towards corrosion protection in 0.5 M NaCl

The corrosion resistance of I-decanthiol (DT), 1,9-nonanedithiol (NDT) and 1,4-benzendimethanethllll lBDMT) sci I' assembled monolayer (SAM) covered copper were investigated using several electrochemical methods Including polarization studies and electrochemical impedance spectroscopy lEIS) in aqueous 0.5 M NaCI solution. The SAM covered surface was characterized by Fourier transform infrared reficetance spectroscopy (FTJR), atomic force microscopy (AFM) and cyclic voltammetry. The inhibition efficiency (IE) of the SAM/copper was investigated by varying: concentration of thiol in solution used for scII' assembly, assembly period for the formation of SAM and effect of solvents (DMF, toluene, ethanol and acetonitrile) for preparing the thiol solution. The inhibition efficiency of the different thiol compounds under similar experimental conditions for copper corrosion was found to be in the following order: NDT > DT > BMDT. The concentration of thiol and self assembly period affect the quality significantly. At the higher concentration, the self asscmbled monolayer was formed immediately after the solution was introduced to a substrate. There was only a marginal elTect of using different solvent for dissolving the thiols on the inhibition efficiency (IE). FTIR and AFM confirm the sciI' assembling of thiols on copper surface